1. Field of the Invention
The present invention relates generally to a process for the production of a non-oriented electrical steel sheet having excellent magnetic properties usable as a core material in an electrical apparatus or equipment. More particularly, the present invention relates to a process for the production of a non-oriented electrical steel sheet having very excellent magnetic properties while exhibiting a remarkably small difference between the magnetic properties of the steel sheet as measured on a plane coincident with the steel sheet in the rolling direction (hereinafter referred to simply as a L direction) and the magnetic properties of the same as measured on the plane coincident with the steel sheet in the direction at a right angle relative to the rolling direction (hereinafter referred to simply as a C direction).
2. Description of the Prior Art
In recent years, many earnest requests for operating an electrical apparatus, electrical equipment or the like at a higher efficiency have been received because of the current worldwide demand to reduce consumption of electricity and energy, and preserve the world environment. In this connection, many requests to improve the magnetic properties of a non-oriented electrical steel sheet widely used as a metallic material for cores incorporated in a large-sized electrical rotary machine, a medium or small-sized transformer or the like have been received from users.
Generally, a method of reducing the watt loss of a non-oriented electrical steel sheet by increasing the content of silicon or aluminum has been hitherto widely employed as a means for improving the magnetic properties of a conventional non-oriented electrical steel sheet from the viewpoint of reducing eddy current loss induced by an increase in electric resistance. However, it has been found that watt loss can practically be reduced but the most significant problem concerning the reduction of the magnetic flux density of the non-oriented electrical steel sheet cannot be resolved by the method as mentioned above. In view of the foregoing circumstances, treatments for reducing the content of carbon, reducing the content of sulfur or adding boron to the steel sheet as disclosed in an official gazette of Japanese Unexamined Publication Patent (Kokai) NO. 54-163720 were employed in addition to a treatment for increasing the content of silicon or aluminum. In spite of the treatments employed in the above-described manner, reduction of watt loss was practically achieved but remarkable effects were not recognized with respect to the magnetic flux density of the non-oriented electrical steel sheet.
As disclosed in official gazettes of, e.g., Japanese Unexamined Publication Patent (Kokai) NO. 58-151453, Japanese Unexamined Publication Patent (Kokai) NO. 59-157259, Japanese Unexamined Publication Patent (Kokai) NO. 61-067753 and Japanese Unexamined Publication Patent (Kokai) NO. 62-180014, a method of improving the magnetic properties of a non-oriented electrical steel sheet by a combination made among the addition of an element of tin, copper or the like by a small quantity and production process conditions have been proposed based on the viewpoint that watt loss and magnetic flux density can simultaneously be improved by developing the texture of the electrical steel sheet to assume a magnetically desirable shape. With the proposed method, however, development of a (111) texture undesirable for the magnetic nature of the non-oriented electrical sheet was actually suppressed but growth of a (100) texture hitherto considered most desirable for the magnetic nature of the non-oriented has not been achieved. Unexpectedly, there appears a problem in that a (110) texture hitherto considered desirable for the magnetic nature of an oriented electrical steel sheet is liable to develop.
On the other hand, a method of producing a non-oriented electrical steel sheet by intensely cold rolling a hot-rolled steel sheet at a high reduction ratio of 85% or more, preferably 90% or more and then annealing the cold-rolled steel sheet under a temperature ranging from 700.degree. C. to 1200.degree. C. and a time ranging from 2 minutes to one hour as disclosed in an official gazette of Japanese Examined Publication Patent (Kokoku) NO. 51-942 has been hitherto employed as means for developing a (100) texture desirable for the magnetic nature of the non-oriented electrical steel sheet. However, since this method requires annealing the cold-rolled steel sheet for a long period of time in addition to intensely cold rolling the hot-rolled steel sheet, employment of the method was very disadvantageous from the viewpoint of practical use of the method because of the problems associated with reduction of productivity, elevation of production cost and installation of an expensive production line.
The present invention has been made with the foregoing in mind and its subject resides in providing a method of producing a non-oriented electrical steel sheet having excellent magnetic properties in a simple manner wherein a difference between the magnetic properties of the electrical steel sheet in the L direction and the magnetic properties of the same in the C direction can be significatly reduced by developing a (100) texture desirable for the magnetic nature of the electrical steel sheet.